Mitogen-activated protein (MAP) kinases comprise a family of protein-serine/threonine kinases, which are highly conserved in protein structures from unicellular eukaryotic organisms to multicellular organisms, including mammals. These kinases, including ERKs, JNKs and p38s, are regulated by a phosphorelay cascade, with a prototype of three protein kinases that sequentially phosphorylate one another. MAPKs transduce extracellular signals into a variety of cellular processes, such as cell proliferation, survival, death, and differentiation. Consistent with their essential cellular functions, MAPKs have been shown to play critical roles in embryonic development, adult tissue homeostasis and various pathologies. In this review, we discuss recent findings that reveal the profound impact of these pathways on chronic inflammation and, particularly, inflammation-associated cancer development.

Eukaryotic DNA replication is tightly restricted to only once per cell cycle in order to maintain genome stability. Cells use multiple mechanisms to control the assembly of the prereplication complex (pre-RC), a process known as replication licensing. This review focuses on the regulation of replication licensing by posttranslational modifications of the licensing factors, including phosphorylation, ubiquitylation and acetylation. These modifications are critical in establishing the pre-RC complexes as well as preventing rereplication in each cell cycle. The relationship between rereplication and diseases, including cancer and virus infection, is discussed as well.

A chimeric protein called Wallerian degeneration slow (Wld^S) was first discovered in a spontaneous mutant strain of mice that exhibited delayed Wallerian degeneration. This provides a useful tool in elucidating the mechanisms of axon degeneration. Over-expression of Wld^S attenuates the axon degeneration that is associated with several neurodegenerative disease models, suggesting a new logic for developing a potential protective strategy. At molecular level, although Wld^S is a fusion protein, the nicotinamide mononucleotide adenylyl transferase 1 (Nmnat1) is required and sufficient for the protective effects of Wld^S, indicating a critical role of NAD biosynthesis and perhaps energy metabolism in axon degeneration. These findings challenge the proposed model in which axon degeneration is operated by an active programmed process and thus may have important implication in understanding the mechanisms of neurodegeneration. In this review, we will summarize these recent findings and discuss their relevance to the mechanisms of axon degeneration.

The M2 proteins of influenza A and B virus, AM2 and BM2, respectively, are transmembrane proteins that oligomerize in the viral membrane to form proton-selective channels. Proton conductance of the M2 proteins is required for viral replication; it is believed to equilibrate pH across the viral membrane during cell entry and across the trans-Golgi membrane of infected cells during viral maturation. In addition to the role of M2 in proton conductance, recent mutagenesis and structural studies suggest that the cytoplasmic domains of the M2 proteins also play a role in recruiting the matrix proteins to the cell surface during virus budding. As viral ion channels of minimalist architecture, the membrane-embedded channel domain of M2 has been a model system for investigating the mechanism of proton conduction. Moreover, as a proven drug target for the treatment of influenza A infection, M2 has been the subject of intense research for developing new anti-flu therapeutics. AM2 is the target of two anti-influenza A drugs, amantadine and rimantadine, both belonging to the adamantane class of compounds. However, resistance of influenza A to adamantane is now widespread due to mutations in the channel domain of AM2. This review summarizes the structure and function of both AM2 and BM2 channels, the mechanism of drug inhibition and drug resistance of AM2, as well as the development of new M2 inhibitors as potential anti-flu drugs.

Microtubules play important roles in mitotic spindle assembly and chromosome segregation to maintain normal cell cycle progression. A number of microtubule-associated proteins have been identified in epithelial and neural cell cultures; however, their physiological significance is not well characterized due to the lack of appropriate in vivo animal models. Nucleolar spindle-associated protein (NuSAP) is a microtubule-binding protein and is reported to be involved in mitosis by cell culture studies. In this report, we identified the zebrafish homologue of human NuSAP and investigated its expression profile and functions. Using in situ hybridization, we demonstrated that transcripts of zebrafish nusap1 are specifically expressed in the retina, forebrain, hindbrain and neural crest. When the in vivo expression of nusap1 was knocked down through antisense oligonucleotide morpholino technology, the morphants of nusap1 showed impaired morphogenesis in the trunk and yolk extension, implying the involvement of Nusap1 in cell migration. Mechanistic studies revealed that nusap1 morphants have an altered expression pattern of neural crest markers crestin and sox9b, but normal expression of blood vessel and notochord markers gata1 and shh. In addition, nusap1 mRNA injection caused serious apoptosis in retina and hindbrain tissue, and these phenotypes can be rescued by co-injection of morpholino against nusap1. These observations not only suggest a role for Nusap1 in connecting apoptosis with cell migration, but also provide strong evidences that Nusap1 is potentially involved in morphogenesis in vertebrates.

Retinitis pigmentosa is a leading cause of blindness and a progressive retinal disorder, affecting millions of people worldwide. This disease is characterized by photoreceptor degeneration, eventually leading to complete blindness. Autosomal dominant (adRP) has been associated with mutations in at least four ubiquitously expressed genes encoding pre-mRNA splicing factors—Prp3, Prp8, Prp31 and PAP1. Biological function of adRP-associated splicing factor genes and molecular mechanisms by which mutations in these genes cause cell-type specific photoreceptor degeneration in humans remain to be elucidated. To investigate the in vivo function of these adRP-associated splicing factor genes, we examined Drosophila in which expression of fly Prp31 homolog was down-regulated. Sequence analyses show that CG6876 is the likely candidate of Drosophila melanogaster Prp31 homolog (DmPrp31). Predicted peptide sequence for CG6876 shows 57% similarity to the Homo sapiens Prp31 protein (HsPrp31). Reduction of the endogenous Prp31 by RNAi-mediated knockdown specifically in the eye leads to reduction of eye size or complete absence of eyes with remarkable features of photoreceptor degeneration and recapitulates the bimodal expressivity of human Prp31 mutations in adRP patients. Such transgenic DmPrp31RNAi flies provide a useful tool for identifying genetic modifiers or interacting genes for Prp31. Expression of the human Prp31 in these animals leads to a partial rescue of the eye phenotype. Our results indicate that the Drosophila CG6876 is the fly ortholog of mammalian Prp31 gene.

Retinoic acid-inducible gene-I (RIG-I) functions as an intracellular pattern recognition receptor (PRR) that recognizes the 5’-triphosphate moiety of single-stranded RNA viruses to initiate the innate immune response. Previous studies have shown that Lys63-linked ubiquitylation is required for RIG-I activation and the downstream anti-viral type I interferon (IFN-I) induction. Herein we reported that, RIG-I was also modified by small ubiquitin-like modifier-1 (SUMO-1). Functional analysis showed that RIG-I SUMOylation enhanced IFN-I production through increased ubiquitylation and the interaction with its downstream adaptor molecule Cardif. Our results therefore suggested that SUMOylation might serve as an additional regulatory tier for RIG-I activation and IFN-I signaling.

Current in vitro assays for the activity of HIV-RT (reverse transcriptase) require radio-labeled or chemically modified nucleotides to detect reaction products. However, these assays are inherently end-point measurements and labor intensive. Here we describe a novel non-radioactive assay based on the principle of pyrosequencing coupled-enzyme system to monitor the activity of HIV-RT by indirectly measuring the release of pyrophosphate (PP_i), which is generated during nascent strand synthesis. The results show that our assay could monitor HIV-RT activity with high sensitivity and is suitable for rapid high-throughput drug screening targeting anti-HIV therapies due to its high speed and convenience. Moreover, this assay can be used to measure primase activity in an easy and sensitive manner, which suggests that this novel approach could be wildly used to analyze the activity of PP_i-generated and ATP-free enzyme reactions.

MHC class II expression is controlled mainly at transcriptional level by class II transactivator (CIITA), which is a non-DNA binding coactivator and serves as a master control factor for MHC class II genes expression. Here, we describe the function of a novel splice-isoform of CIITA, DC-expressed caspase inhibitory isoform of CIITA (or DC-CASPIC), and we show that the expression of DC-CASPIC in DC is upregulated upon lipopolysaccharides (LPS) induction. DC-CASPIC localizes to mitochondria, and protein-protein interaction study demonstrates that DC-CASPIC interacts with caspases and inhibits its activity in DC. Consistently, DC-CASPIC suppresses caspases-induced degradation of nitric oxide synthase-2 (NOS2) and subsequently promotes the synthesis of nitric oxide (NO). NO is an essential regulatory molecule that modulates the capability of DC in stimulating T cell proliferation/activation in vitro; hence, overexpression of DC-CASPIC in DC enhances this stimulation. Collectively, our findings reveal that DC-CASPIC is a key molecule that regulates caspases activity and NO synthesis in DC.